Patent Literature 1 discloses an exemplary hydraulic brake device configured to control vehicle braking force in cooperation with a regeneration brake device. This device includes a fluid pressure generator configured to generate, in a master cylinder, a basal fluid pressure as a fluid pressure corresponding to driver's brake operation, and a brake actuator configured to adjust a differential pressure between the master cylinder and a wheel cylinder provided for a wheel.
The fluid pressure generator includes the master cylinder as well as a booster device configured to assist driver's brake operation force. In the master cylinder, the basal fluid pressure is not increased until a shift amount of a master piston configured to shift in accordance with brake operation force assisted by the booster device reaches a predetermined amount. When the brake operation force increases and the shift amount of the master piston reaches or exceeds the predetermined amount, the basal fluid pressure is increased in accordance with the difference obtained by subtracting the predetermined amount from the shift amount and the wheel cylinder is supplied with an amount, corresponding to the basal fluid pressure, of brake fluid via the brake actuator. The “shift amount of the master piston” herein indicates the amount of shift from an initial position of the master piston while a brake is not operated.
In such a hydraulic brake device, the brake actuator is actuated to apply, to a vehicle, braking force corresponding to a difference obtained by subtracting regeneration braking force applied from the regeneration brake device to the vehicle from required braking force corresponding to a driver's brake operation amount. Braking force applied from the hydraulic brake device to a vehicle will be referred to as “hydraulic braking force”.
Regeneration braking force applied from the regeneration brake device to the vehicle is harder to control than hydraulic braking force applied from the hydraulic brake device to the vehicle. Driver's brake operation thus reduces vehicle body speed. When the vehicle body speed becomes not more than predetermined speed, the regeneration braking force is gradually decreased and the hydraulic braking force is gradually increased in accordance with the reduction in vehicle body speed. Such control is a so-called reallocation control. By the reallocation control, the regeneration braking force becomes “zero (0)” and the hydraulic braking force becomes equal to the required braking force corresponding to the driver's brake operation before the vehicle stops.